and they have sent lots of money to scott brown, millions of dollars, and, look, scott brown's been working with the folks on wall street for a long time. >> reporter: wall street is republican senator scott brown's biggest contributor. the financial sector donated more than $2.5 million to his reelection campaign. but in 2010, brown cast the tie- breaking vote to pass wall street reforms. >> i don't owe anybody anything because nobody helped me get down there except the people of massachusetts. >> reporter: the 53-year-old is a moderate republican. he's trying to become the first massachusetts republican to win a full term to the u.s. senate since 1972. what is at stake here? >> if you figure out where the united states senate stands right now, basically you have extremes on both sides. so by sending professor warren down there as an extremist, ultra liberal-- i mean there's no argument there-- and putting her into that mixer where she'll be 100% with her party, how does that solve problems? >> reporter: this particular seat could help determine who controls the senate. isn't that what thi